1. Field of the Invention
The present invention generally relates to a broadcast signal receiving device and a method. More specifically, the present invention relates to a broadcast signal receiving device and a method for receiving digital broadcast signals.
2. Background Information
In recent years, digital broadcast signals that conform to ATSC (Advanced Television Systems Committee) standards have been broadcast from broadcasting stations in North America. Broadcast signal receiving devices (or set-top boxes, hereinafter “STB”) are becoming more popular. The STB receives the digital broadcast signals and converts the digital broadcast signals into signals that can be received by television receivers that handle existing NTSC (National Television Systems Committee) analog broadcasts.
In the digital broadcasts that conform to ATSC standards, the digital broadcast signals are transmitted on physical channels that differ from the physical channels of analog broadcast signals. A single physical channel contains one or more sub-channels used to transmit one or more types of content. Virtual channel numbers are assigned to the sub-channels. The virtual channel numbers include a sub-channel number and a number that is the same as the physical channel number of the analog broadcast that is transmitted from the same broadcasting station or from a broadcasting station in the same broadcast network. Accordingly, virtual channels are constructed in a hierarchical manner from the physical channels and the sub-channels.
The digital broadcast signals include video signals, audio signals and control signals. In the digital broadcasts conforming to ATSC standards, a PSIP (program and system information protocol) is obligatorily attached to the control signals. The PSIP contains information relating to the virtual channel number and the name of the broadcasting station. A control unit of the STB specifies the virtual channel number that is received by referring to a VCT (virtual channel table) that is obtained by acquiring and analyzing the PSIP. Since the virtual channels are constructed in the hierarchical manner from the physical channels and the sub-channels and the construction is complex, it is difficult for users to understand the construction of a channel that is selected by the users.
In the STB, a channel map (or channel table) is provided in which physical channel numbers, virtual channel numbers and sub-channel numbers are registered. The channel map is opened in a RAM of the STB and used when channels are shifted up or down.
Specifically, with a conventional STB, categories of the digital broadcasts indicating television broadcasting, radio broadcastings or data broadcasting are selected by keys. When an up or down key is pressed in a state in which one of the categories has been selected, only channels belonging to the one of the categories are successively selected (see Japanese Laid-Open Patent Application No. 2002-77748, for example).
With another conventional STB, a channel map is created. The channel map indicates whether or not each of channels is being broadcast. When a channel up or down key is operated by a user, only channels being broadcast are selected by using the channel map (see Japanese Laid-Open Patent Application No. 2004-364216).
In the digital broadcasts in the United States, especially cable digital broadcasts, radio channels (hereinafter “audio channels”) mainly broadcasting audio are mixed with ordinary channels such as television channels or the like (hereinafter “video channels”). Some broadcasting stations broadcast many of the audio channels. If the audio channels are registered in the channel map mixed with the video channels, it becomes difficult to select a desired video channel using a channel up or down key. As a result, the STB becomes difficult to use.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved broadcast signal receiving device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.